The present invention relates to an improved plug which can be installed into a pipe with an installation key but can be removed only with a removal key, and it also relates to an improved structure for aligning a key having a curved ridge with the mating curved groove of a plug or a nut.
By way of background, in certain instances it is necessary to have a type of plug which can be installed in a pipe by many people but which can be removed only by a select few people having a special removal key. This type of plug is generally used where it is necessary to shut off a gas meter or water meter. In situations of this type the plugs can be installed by numerous personnel who are sent out on routine calls for this purpose. However, it is desirable that the task of removing the plugs be delegated to only a few select personnel to whom removal keys are entrusted. By following this procedure, there need be only very few removal keys in existence, and therefore the risk of these keys being duplicated for unauthorized removal of plugs is greatly diminished.